The catalytic converter is a part of the exhaust system that is located after the exhaust manifold and before the muffler. The active part of a catalytic converter is a honey-comb matrix coated with precious metals through which the exhaust flows. Its main job is to react with and remove harmful gases from the exhaust stream to improve the vehicle’s emissions.
Laws vary from state to state, and sometimes, vary across different regions within a state. But usually, it is required that a vehicle have a functional catalytic converter in order for it to be sold or operated. Exceptions are for older vehicles that were designed and sold without catalytic converters originally.
Cost of Catalytic Converter Replacement
The cost of vehicle repairs or parts replacement is dependent on several factors such as the type and model of the vehicle, the type, and quality of the parts to be used, as well as the location of the auto shop doing the service.
To be able to differentiate the prices based on these factors, below are some estimates of the catalytic converter replacement cost for some common vehicles using $100 an hour as a labor rate:
- For a 2005 Honda CR-V with a 2.4-liter engine, the labor time is estimated at around 0.6 of an hour. A factory part costs about $2726, a CARB compliant Walker replacement costs about $304, and a non-certified Davico replacement costs about $188. The total cost to complete the job would be about $2786 using OE parts, about $364 using a certified aftermarket part, or about $248 using a non-certified part.
- For a 2007 Jeep Wrangler with a 3.8-liter engine, the labor time is estimated at around 1.8 hours. A factory replacement part costs about $945, an AP CARB compliant part costs about $864, and an uncertified Davico part costs about $424. The total cost to complete the job would be about $1,125 using OE parts, about $1,044 using certified aftermarket parts, or about $604 using uncertified parts.
- For a 2006 Chevrolet 1500 four-wheel-drive truck with a 5.3-liter engine, the labor time is estimated at around 1.4 hours. A factory replacement assembly costs about $459, a Walker CARB certified part costs about $460, and a Walker non-certified part costs about $322. The total cost to complete the job would be about $599 using factory parts, about $600 using certified aftermarket parts, and about $462 using non-certified parts.
- For a 2005 Nissan Maxima with a 3.5-liter transverse V-6 engine, there is a front and a rear catalytic converter, replaceable separately. The labor time to replace the front catalytic converter is 1 hour, a factory catalytic converter price is about $740, and a Walker CARB compliant part costs about $256. The total cost to complete the job for the front would be about $840 using factory parts and about $356 using certified aftermarket parts. For this vehicle, the labor time to replace the rear catalytic converter is estimated at 3.4 hours. A factory replacement part costs about $740, and a Walker CARB compliant part costs about $244. The total cost to complete the job for the rear would be about $1,080 using factory parts, and about $584 using certified aftermarket parts.
In all cases, there is the likelihood of some relatively small additional costs for gaskets and hardware.
It is also fairly common to replace the O2 sensors with the catalytic converter. Ordinarily, they can be removed from the old part and installed in the new part (the labor being included in the job cost).
However, heat issues can cause them to seize up or have damaged threads, and sometimes, if a catalytic converter is being replaced for contamination issues, it’s prudent to assume that the O2 sensor may also be affected.
Aftermarket Versus Original Equipment
As far as doing the job it is designed to do, one of the most important things about a replacement catalytic converter is something you can’t see or directly test – its oxygen capacity. This determines how effectively the cat can act on the vehicle’s exhaust stream.
A vehicle with a large displacement engine moves more air and requires a larger capacity catalytic converter, while the reverse is true for a smaller engine. The engine’s computer uses the oxygen sensor data to monitor the oxygen capacity of the catalytic converter.
This, then, leads to an unfortunately common issue. While an OE replacement catalytic converter will have the same capacity as the original and satisfy the expectations of the PCM, not all aftermarket cats are tested for capacity.
The expensive part of a catalytic converter is the catalyst itself which incorporates precious metals in a matrix. Economizing on this saves costs, but decreases capacity.
It is possible then to buy and install a new cat, and after a short time, have the same fault code come back that leads to the replacement. The most likely case is that the cat doesn’t meet the capacity requirements for the vehicle.
The best way to be safe is to either choose an OE catalytic converter or an aftermarket CARB compliant converter. This means that it has been tested and meets the strict California emissions requirement that a replacement converter has at least the capacity of the original part.
In several states, this is a requirement. However, it varies from state to state (and year to year as well). On the general principle that it’s best to avoid having to do an expensive job twice, going with either a CARB-compliant or an OE catalytic converter is the prudent choice.
The least expensive way to replace a catalytic converter is to install a “universal” replacement part which is usually made to be welded into the place of the original or a slightly more expensive non-certified part.
Universal catalytic converters are generally only installed at muffler shops that have the proper pipe-forming and welding equipment. Non-certified parts are usually bolt-on replacements that most shops could install.
It’s best to be sure of the warranty if either of these is done. Though, if the part works without issue for the first month or two, that usually means it will be fine for the long term.
While they can cause issues, the cost savings are usually significant where it can legally be done.
Catalytic Converter Replacement
In most cases, an engine light will be the only indication of catalytic converter failure; the codes P0420 and P0430 being the common ones. The general rule for diagnosis is to repair any other engine fault codes first, rule out exhaust leaks, verify if the converter fault is persistent, and then, replace the catalytic converter.
Most of the time, the catalytic converter is a bolt-on part and not too hard to access. Replacement can still be problematic due to the high temperatures it runs at.
Exhaust-specific fasteners are usually used, which manage heat well but are more prone to rust. It’s very common to replace the fastening bolts and hardware along with the catalytic converter. It’s also very common to have the old parts break, shear off, have to be removed with a torch or cutting tool, etc.
On a V-6 or V-8 engine, there is usually one catalytic converter for each bank of cylinders, and these are often not replaceable separately. A pre-formed Y-pipe with two catalytic converters is more common; though an expensive OE arrangement.
In any case, if one catalytic converter has failed due to age or operating conditions, the other is likely in the same shape.
What a Catalytic Converter Does
Most modern catalytic converters can also be called “three-way” converters. This means that they accomplish three different specific operations on the exhaust stream.
The first is that they strip the oxygen molecule from nitrogen oxides. Nitrogen oxide is a product of the burning of hydrocarbons and is the main ingredient of the brown hazy “smog”; a lung and eye irritant. The byproducts of this are harmless nitrogen and a free oxygen molecule.
The second operation is to add an oxygen molecule to carbon monoxide which is another very harmful product of burning hydrocarbons. Carbon monoxide is a particularly deadly gas, but adding a molecule of oxygen to it creates carbon dioxide.
This has problems in itself, of course (being the infamous CO2), but it is more inert and not immediately harmful in low concentrations. The third operation also consumes free oxygen to convert unburned hydrocarbons into CO2 and H2O.
The main way that the PCM determines the efficiency of a catalytic converter is by looking at data from the O2 sensors before and after the catalytic converter and using that data to infer the oxygen capacity of the converter. This is more or less its capacity to perform the last two operations.
Problems that Can Lead to Catalytic Converter Failure
The conversion of unburned hydrocarbons in the exhaust stream is an essential role of the catalytic converter. However, it can also lead to problems if they are excessive as the process itself generates heat.
Hydrocarbons in the exhaust stream can come normally from hard acceleration or less than perfect combustion. They can also form from various engine problems (both mechanical and sensor-related) leading to a too rich fuel mixture or poor combustion, or engine misfires.
In small amounts or for brief periods, usually, no harm is done. Nevertheless, the catalyzing of hydrocarbons creates heat, and it is possible for the catalytic converter to overheat if it’s exposed to too much unburned fuel.
In the worst cases, the core can melt down and obstruct the exhaust flow. If a catalytic converter needs to be replaced due to overheating, it’s always a good practice to diagnose and repair any running issues it has at the same time.
Oil burning can also cause issues. Every engine burns a little bit of oil by design as oil lubricates the cylinder walls as the rings move against them to prevent wear. As the rings age and especially if oil changes are neglected allowing thickened oil to gum up the free movement of the rings, however, more oil can be left on the cylinder walls than designed.
Older and neglected engines tend to burn more oil and that can cause problems with the catalytic converter. This typically leaves carbon deposits on the active matrix that interferes with the effective operation.
This can lead to a check engine light for inadequate catalytic converter efficiency. If an oil consumption problem leads to a failed catalytic converter, then, the realistic long-term solution can be more involved than simply replacing the catalytic converter.
Coolant in the exhaust stream can also damage a catalytic converter by creating a barrier coating of contaminants on the surfaces of the matrix that prevent its operation in the same way that an oil consumption problem can cause a problem.
This coolant would usually only come from a head gasket fault, and this can leak very slowly over a long period of time. One of the things that should be ruled out or looked at when replacing a failed catalytic converter is whether the engine has a problem with coolant loss which might need to be diagnosed.